Distinctive hydration dynamics around highly coordinated Cu2+/Zn2+-chloride complexes: A molecular dynamics simulation study

Abstract

The existence of highly coordinated dication-chloride complexes and hydration characteristics around these species remain controversial. In this work, molecular dynamics simulations were used to investigate the stability of [CuCl4]2− and [ZnCl4]2− complexes in aqueous solution at various temperatures and electric fields. The results exhibit the presence of [CuCl4]2− and [ZnCl4]2− complexes in aqueous solution. For [CuCl4]2− and [ZnCl4]2− complexes, there is no overlap of the inner hydration shells, which is different from [CaClx]2-x (x = 4– 6) complexes. Our results show that the existence of [CuCl4]2− and [ZnCl4]2− species can be attributed to the hydration dynamics of their second shell. The dynamic rotation of hydration bonds between water molecules and Cl− ions of [CuCl4]2− or [ZnCl4]2− clusters can prolong the residence of the water molecules in the second shell, and promote the presence of [CuCl4]2− and [ZnCl4]2− species in aqueous solution. The dynamic rotation of water molecules also results in the relative separation of [CuCl4]2− or [ZnCl4]2− clusters with the bulk phase. Compared with hydrated Cu2+ ion, the fast diffusion of [CuCl4]2− cluster indicates that the interaction of hydrated [CuCl4]2− cluster with bulk phase is relatively weak.